A patient on maintenance hemodialysis developed an acute encephalopathy closely related to a rapid increase in serum aluminum levels. Aluminum hydroxide and sucralfate had been given in large amounts for the treatment of a gastrointestinal bleeding episode. The breach of the gastrointestinal barrier to aluminum absorption, the increase in gastric pH caused by cimetidine, and the presence of gastric telangiectasia acting together in a uremic patient could have precipitated the acute aluminum encephalopathy.